Fossil Ammonite (Sphenodiscus) & Gastropod Association - South Dakota

This is a cluster of ammonite (Sphenodiscus lenticularis) and gastropod fossils from the Fox Hills Formation of South Dakota. The ammonites and gastropods have been meticulously prepped to expose them from the hard concretion they were found in. One edge of the rock has been cut flat to facilitate aesthetic presentation without the need for a display stand.

Ammonites were predatory cephalopod mollusks that resembled squids with spiral shells. They are more closely related to living octopuses, though their shells resemble that of nautilus species. True ammonites appeared in the fossil record about 240 million years ago during the Triassic Period. The last lineages disappeared 65 million years ago at the end of the Cretaceous.

What an ammonite would have looked like while alive.
What an ammonite would have looked like while alive.

These 70 million year old ammonites lived when South Dakota was a shallow inland sea. They were found preserved in concretions when split open. They then had to be hand-prepared to remove the hard rock surrounding them from their shells, a very time consuming task.
SOLD
DETAILS
SPECIES
Sphenodiscus lenticularis & Unidentified Gastropods
LOCATION
North Central, South Dakota
FORMATION
Fox Hills Formation
SIZE
Ammonites: 1.5", 1" & .8" , Rock: 3.8 x 2.9"
ITEM
#189357
GUARANTEE
We guarantee the authenticity of all of our
specimens. Read more about our
Authenticity Guarantee.